The present invention relates to an apparatus and a method for continuously manufacturing a tubular member by overlapping and bonding flexible webs or strips as a plurality of layers.
Methods and apparatus for forming tubular members are known as proposed in Japanese Patent Publications Nos. 57-61582 and 60-35254 corresponding respectively to U.S. Pat. Nos. 4,474,564 and 4,353,764, both issued to Sireix.
According to the proposed methods, a plurality of flexible webs or strips are overlapped in transversely shifted positions so that their side edges are shaped like a staircase. The overlapped webs are first bonded at narrow areas thereof positioned intermediate between their opposite side edges, and then progressively bent around a mandrel into a tubular form. At the same time, the widths of the bonded areas of the overlapped webs are progressively increased toward the opposite side edges until the opposite side edges are joined. Then, the opposite edges of the positionally shifted webs are held in abutment against and coupled to each other thereby to continuously form a complete tubular member, which is withdrawn along the mandrel and then cut off to a suitable length.
By progressively increasing the bonded areas when forming the tubular member, the bonded areas of the webs are prevented from being wrinkled.
Where the adhesive used is a water-soluble adhesive, and when the bonded areas are progressively increased, the bonded strips are allowed to be positionally displaced for a relatively long period of time after they have been bonded, because the adhesive is of a liquid state. Therefore, no special care is required during the bonding process at the time of progressively increasing the bonded areas.
However, use of the water-soluble adhesive is problematic for the following reasons. A long period of time is required for the water-soluble adhesive to be dried. In case the formed tubular member is used as the barrel of a container for storing a liquid, a water-resistant layer must be added as an outermost or innermost layer. With the water-resistant layer added, the adhesive cannot easily be dried. Therefore, if a tubular member for use as a liquid container is to be manufactured, then it is preferable to employ a hot-melt adhesive which does not need to be dried.
When the hot-melt adhesive is applied to form a tubular member form webs, the webs are firmly secured to each other at the same time that the they are bonded by the hot-melt adhesive. Unless, therefore, the webs are uniformly bonded even at localized areas thereof, the webs are subjected to wrinkles, giving rise to non-bonded areas which tend to reduce the pressure resistance of the produced tubular member. Thus, with the use of the hot-melt adhesive, any tubular member of high quality cannot be formed simply by progressively increasing the bonded areas.
As described above, it is time-consuming for the water-soluble adhesive to be dried before a tubular member is formed. Accordingly, if the tubular member being formed is to be continuously cut to desired lengths, the speed at which the tubular member is formed should be lowered.
The hot-melt adhesive is advantageous over the water-soluble adhesive since the speed at which the tubular member is formed can be increased with the hot-melt adhesive being relied upon.
Even where the hot-melt adhesive is used, however, because a number of webs are bonded as layers by the hot-melt adhesive, it takes some time before the adhesive layers between the webs bond them to the extent that can withstand tensile forces which will be applied to the formed tubular member. In the tubular member of this structure, the opposite side edges of the webs are finally bonded. Consequently, unless these portions are reliably bonded together, the joined areas may be opened and the tubular member may be broken when the tubular member is withdrawn and cut off. To allow the tubular member to be withdrawn and cut off without damage or breakage, a period of time should be permitted to elapse until the joined areas are completely bonded together. This prevents the rate of production of the tubular member from being increased.
According to Japanese Patent Publication No. 60-35254, the joined opposite side edges of the webs are held in abutment against each other as described above. This is advantageous in that even if the side edges of the webs are positionally displaced slightly when forming the tubular member, they can form joined areas.
With the structure of the abutting joined areas, however, it cannot provide a sufficient degree of pressure resistance when the tubular member is used as the barrel of a pressure-resistant container such as for containing a carbonated beverage.
There has been proposed a tubular member as disclosed in Japanese Laid-Open Utility Model Publication No. 61-43114. According to the disclosed arrangement, and as shown in FIG. 26 of the accompanying drawings of the present application, the side edges x1, x2, y1, y2, z1, z2 of webs X, Y, Z are overlapped with the outer side edge x2 abutting against the inner side edge y1 and the outer side edge y2 abutting against the inner side edge z1 for increasing the pressure resistance of the joined areas.
To accomplish the illustrated structure, the side edges of the webs X, Y, Z should be positioned such that the outer side edge x2 abuts against the inner side edge y1 and the outer side edge y2 abuts against the inner side edge z1. Otherwise, gaps would be created between the outer side edge x2 and the inner side edge y1 and between the outer side edge y2 and the inner side edge z1, thereby reducing the pressure resistance.
In the case where the formed tubular member is used as the barrel of a container of a beverage such as a carbonated beverage, an innermost layer U is required to give the container barrel water resistance and sealing capability.
The innermost layer U comprises a water-resistant layer as a gas barrier. The layer U and the webs X, Y, Z are wound around a mandrel to form a tubular member, and the opposite side edges of the layer U are joined to each other for sealing capability. More specifically, as shown in FIG. 26, the innermost layer U is formed as a tubular body, and its opposite side edges u1, u2 mate against each other, are bonded to each other, then folded to one side, and finally bonded to an outer surface of the tubular body.
Prior to the formation of the tubular member from the outer webs X, Y, Z, the innermost layer U is bent to its form along the mandrel so that the joined side edges u1, u2 will be disposed inside of the tubular member.
The webs U, X, Y, Z used to form the tubular member are in the form of elongate strips, which are continuously supplied along the mandrel. It is efficient to form the tubular member from the webs X, Y, Z after the innermost layer has been formed from the web U. Therefore, an apparatus is required to form the innermost layer.